This invention relates to a plate-type heat exchanger, and particularly relates to measures for reducing a pressure loss of a fluid.
Various kinds of heat exchangers have conventionally been used in air conditioning systems, refrigerating systems, chilling systems and the like. Out of these heat exchangers, for example, a plate-type heat exchanger is known as a compact heat exchanger having a large coefficient of overall heat transmission as disclosed in xe2x80x9cShin-ban, Dai 4-han, Reito Kucho Binran (Ohyo-hen)xe2x80x9d pp. 82, edited by Japan Society of Refrigerating and Air Conditioning Engineers.
As shown in FIG. 10, the plate-type heat exchanger is constructed so that a plurality of heat transfer plates (p), (p), . . . are piled one after another between two frames (f1), (f2).
Each of the heat transfer plates (p) is formed of a planar metal plate. The periphery of the heat transfer plate (p) engages the peripheries of the adjacent heat transfer plates (p) and the engagement portions are joined together by brazing. This provides an integral structure of the plurality of heat transfer plates (p). A first flow channel (a1) and a second flow channel (b1) are alternately formed in respective spaces between the adjacent heat transfer plates (p).
Four corners of each heat transfer plate (p) are provided with respective openings (a), (b), (c), (d) forming an inlet or outlet of the first flow channel (a1) or an inlet or outlet of the second flow channel (b1). By providing seals (e) surrounding the respective openings (a), (b), (c), (d), a first inflow space (a2) and a first outflow space (a3) each communicating with the first flow channel (a1) alone and a second inflow space (b2) and a second outflow space (b3) each communicating with the second flow channel (b1) alone are formed. The first fluid flows through the flow channel (a1) as shown in solid arrows in FIG. 10, the second fluid flows through the flow channel (b1) as shown in broken arrows in FIG. 10, and the first and second fluids heat-exchanges with each other via the heat transfer plates (p).
The conventional plate-type heat exchanges have used so-called longitudinally elongated heat transfer plates (p), i.e., heat transfer plates (p) having their longitudinal length considerably greater than their lateral length. In other words, conventionally, heat transfer plates (p) having a large ratio of the longitudinal length to the lateral length, i.e., a large aspect ratio, have been used.
However, the flow channel (a1), (b1) formed by the heat transfer plates (p) of large aspect ratio has a large channel length. Therefore, such conventional plate-type heat exchangers have caused large pressure losses of the fluid in the flow channel (a1), (b1).
Particularly in the case of using a fluid such as fluorocarbon refrigerant involving a phase change during heat exchange, a pressure loss in the flow channel becomes larger as compared with the case of using a fluid such as water in a single phase. The reason for this is that a two-phase flow has a larger pressure loss per unit flow rate than a single-phase flow. Accordingly, a large driving force has been required in order to pass such a two-phase refrigerant through the flow channel.
In addition, such a refrigerant decreases its temperature with decrease in its pressure. Therefore, if the pressure loss of the refrigerant is large, temperature profile in the heat exchanger becomes large in a flowing direction of the fluid. This invites a problem of decreasing a heat exchanger effectiveness.
Depending upon the type of apparatus in which the plate-type heat exchanger is mounted, for example, the type of air conditioner, a severe constraint may be placed on pressure loss in the flow channel. In such a case, conventionally, the number of heat transfer plates is increased to decrease the flow rate of refrigerant per flow channel thereby decreasing a pressure loss. Such a method, however, necessities a large number of heat transfer plates, which invites rise in cost of the air conditioner.
The present invention has been made in view of the above problems and therefore has its object of providing a plate-type heat exchanger having a small pressure loss of a fluid at low cost.
To attain the above object, in the present invention, the aspect ratio of the heat transfer plate is decreased so that the channel length is decreased without decreasing its heat transfer area.
More specifically, a plate-type heat exchanger according to the present invention in which a first flow channel (A) or a second flow channel (B) is formed between adjacent two of plural piled heat transfer plates (P1, P2; P3, P4), the first and second flow channels (A, B) allow respective first and second fluids to flow therethrough in a longitudinal direction of the heat transfer plate (P1, P2; P3, P4) and the first and second fluids are heat-exchanged with each other via the heat transfer plates (P1, P2; P3, P4), is characterized in that each of the heat transfer plates (P1, P2; P3, P4) is formed so that a longitudinal length (L) thereof is equal to or smaller than two times a lateral length (W) thereof.
Each of the heat transfer plates (P1, P2; P3, P4) may be formed so that the longitudinal length (L) thereof is not smaller than the lateral length (W) thereof and not larger than two times the lateral length (W).
Around an inlet (21a, 21b, 23a, 23b) of the at least one flow channel (A, B) formed in each of the heat transfer plates (P1, P2, P3, P4), a drift suppressing rib set (50a, 50b, 60a, 60b) including a plurality of ribs (51 through 58) may be formed to introduce the fluid from the inlet (21a, 21b, 23a, 23b) uniformly into the flow channel (A, B).
Each of the heat transfer plates (P1, P2; P3, P4) may be provided with an inlet (21a, 21b) and an outlet (22a, 22b) of the first flow channel (A) at respective ends in a longitudinal direction (Y) of the heat transfer plate (P1, P2; P3, P4) and provided with an inlet (23a, 23b) and an outlet (24a, 24b) of the second flow channel (B) at respective other ends in the longitudinal direction (Y) of the heat transfer plate (P1, P2; P3, P4), a primary heat transfer enhancement surface (20a, 20b) for enhancing heat exchange by giving disturbance to the flow of each fluid may be formed at least between the inlet (21a, 21b, 23a, 23b) and the outlet (22a, 22b, 24a, 24b) of each of the flow channels (A, B) of the heat transfer plate (P1, P2; P3, P4), and the longitudinal length of the primary heat transfer enhancement surface (20a, 20b) may be equal to or smaller than two times the lateral length thereof.
The inlet (21a, 21b) and the outlet (22a, 22b) of the first flow channel (A) may be provided in cater-cornered opposite positions of the heat transfer plate (P1, P2; P3, P4), and the inlet (23a, 23b) and the outlet (24a, 24b) of the second flow channel (B) may be provided in another cater-cornered opposite positions of the heat transfer plate (P1, P2; P3, P4).
The inlet (21a, 21b) and the outlet (22a, 22b) of the first flow channel (A) may be provided in cater-cornered opposite positions of the heat transfer plate (P1, P2; P3, P4), the inlet (23a, 23b) and the outlet (24a, 24b) of the second flow channel (B) maybe provided in another cater-cornered opposite positions of the heat transfer plate (P1, P2; P3, P4), and each of the heat transfer plates (P1, P2; P3, P4) may be provided with: seals (12a through 15b), formed to surround the inlet (21a, 21b, 23a, 23b) and the outlet (22a, 22b, 24a, 24b) of each of the flow channels (A, B) and rise on the front side or back side of the heat transfer plate (P1, P2; P3, P4), for preventing the first and second fluids from flowing into the second flow channel (B) and the first flow channel (A), respectively, by engaging one of the adjacent heat transfer plates (P1, P2; P3, P4); a primary heat transfer enhancement surface (20a, 20b) formed in a longitudinal midportion of the heat transfer plate (P1, P2; P3, P4), for enhancing heat exchange by giving disturbance to the flow of each fluid vertically flowing on the heat transfer plate (P1, P2; P3, P4); and an auxiliary heat transfer enhancement surface (30a, 30b), formed between the seals (12a through 15b) of the heat transfer plate (P1, P2; P3, P4) and the primary heat transfer enhancement surface (20a, 20b), for enhancing heat exchange by giving disturbance to the flow of the fluid diverging from the inlet (21a, 21b, 23a, 23b) toward the primary heat transfer enhancement surface (20a, 20b) or the flow of the fluid converging from the primary heat transfer enhancement surface (20a, 20b) toward the outlet (22a, 22b, 24a, 24b).
The inlet (21a, 21b) and the outlet (22a, 22b) of the first flow channel (A) may be provided in cater-cornered opposite positions of the heat transfer plate (P1, P2; P3, P4), the inlet (23a, 23b) and the outlet (24a, 24b) of the second flow channel (B) maybe provided in another cater-cornered opposite positions of the heat transfer plate (P1, P2; P3, P4), and each of the heat transfer plates (P1, P2; P3, P4) may be provided with: seals (12a through 15b), formed to surround the inlet (21a, 21b, 23a, 23b) and the outlet (22a, 22b, 24a, 24b) of each of the flow channels (A, B) and rise on the front side or back side of the heat transfer plate (P1, P2; P3, P4), for preventing the first and second fluids from flowing into the second flow channel (B) and the first flow channel (A), respectively by engaging one of the adjacent heat transfer plates (P1, P2; P3, P4); a primary heat transfer enhancement surface (20a, 20b), formed in a longitudinal midportion of the heat transfer plate (P1, P2; P3, P4), for enhancing heat exchange by giving disturbance to the flow of each fluid vertically flowing on the heat transfer plate (P1, P2; P3, P4); an auxiliary heat transfer enhancement surface (30a, 30b), formed between the seals (12a through 15b) of the heat transfer plate (P1, P2; P3, P4) and the primary heat transfer enhancement surface (20a, 20b), for enhancing heat exchange by giving disturbance to the flow of the fluid diverging from the inlet (21a, 21b, 23a, 23b) toward the primary heat transfer enhancement surface (20a, 20b) or the flow of the fluid converging from the primary heat transfer enhancement surface (20a, 20b) toward the outlet (22a, 22b, 24a, 24b); and a plurality of ribs (51 through 58), formed around each of the inlets (21a, 21b, 23a, 23b), for introducing the fluid flowing from each of the inlets (21a, 21b, 23a, 23b) uniformly in respective predetermined directions.
The plurality of ribs (51 through 58) may be arranged at irregular intervals so that an interval between the ribs (53 through 56) intermediate the ends of the rib set is narrower than that between the ribs (51, 52, 57, 58) closer to the ends of the rib set.
The plurality of ribs (51 through 58) may be formed so that the rib (53 through 56) intermediate the ends of the rib set is broader than the rib (51, 52, 57, 58) closer to the ends of the rib set.
The plurality of ribs (51 through 58) may be arranged substantially radially in the flow channel (A, B) downstream from the inlet (21a, 21b, 23a, 23b) and the length of the rib (51, 52, 57, 58) closer to the ends of the rib set may be larger than that of the rib (53 through 56) intermediate the ends of the rib set.
The plurality of ribs (51 through 58) may be arranged substantially radially in the flow channel (A, B) downstream from the inlet (21a, 21b, 23a, 23b) and the length of the rib (51, 52, 57, 58) closer to the ends of the rib set may be smaller than that of the rib (53 through 56) intermediate to the ends of the rib set.
At least one of the first fluid flowing through the first flow channel (A) and the second fluid flowing through the second flow channel (B) may be a fluid for providing heat exchange involving a phase change.
When the aspect ratio is decreased, the width of the flow channel (A, B) is increased but the length thereof is decreased. As a result, the channel length can be decreased without decreasing the heat transfer area. Therefore, without increasing the number of heat transfer plates, a pressure loss of each fluid can be decreased while maintaining the amount of heat exchange.
When the aspect ratio is set at a value of between 1 and 2, a drift due to increase in lateral length (W) can be suppressed and a suitable aspect ratio having a small pressure loss of the fluid can be obtained.
Furthermore, since a drift can be suppressed by the plurality of ribs (51 through 58), the fluid uniformly flows through the flow channel (A, B).
Moreover, the first fluid in the first flow channel (A) and the second fluid in the second flow channel (B) flows through the respective flow channels (A, B) along the diagonal of the heat transfer plate (P1, P2; P3, P4). Therefore, even if the aspect ratio is small, the fluid can flow relatively uniformly through the flow channel (A, B).
Further, since the flow is disturbed in the primary heat transfer enhancement surface (20a, 20b) and the auxiliary heat transfer enhancement surface (30a, 30b), heat exchange can be enhanced. It is to be noted that though the fluid tends to increase its pressure loss due to the disturbance of flow, a pressure loss of the fluid in the primary heat transfer enhancement surface (20a, 20b) can be decreased by setting the longitudinal length of the primary heat transfer enhancement surface (20a, 20b) at a value equal to or smaller than two times the lateral length thereof. Accordingly, heat exchange can be enhanced without largely increasing the pressure loss.
Furthermore, the plurality of ribs (51 through 58) are arranged at irregular intervals. At intermediate locations of the rib set where the fluid is essentially easy to flow, the flow of fluid is suppressed since the interval between the ribs (53 through 56) is narrow. On the other hand, at the ends of the rib set where the fluid is essentially hard to flow, the flow of fluid is accelerated since the interval between the ribs (51, 52, 57, 58) is broad. As a result, the fluid can flow uniformly through the entire flow channel and a drift can securely be prevented.
Moreover, when the fluid performing heat exchange involving a phase change flows, the effect of decreasing pressure loss in the flow channel can be more extensively exerted since such fluid has a property of a relatively large pressure loss.
According to the present invention, the length of the flow channel can be decreased without decreasing the heat transfer area. Therefore, a pressure loss of the fluid can be decreased without increasing the number of heat transfer plates. This makes it possible to construct a heat exchanger having a small pressure loss at low cost.
Further, if the aspect ratio is set at a value of between 1 and 2, there can be obtained a heat transfer plate suitable for decreasing a pressure loss while suppressing a drift of the fluid.
Furthermore, since the plurality of ribs prevents a drift of the fluid, increase in drift due to decrease in aspect ratio can be suppressed.
Moreover, since each fluid flows along the diagonal of the heat transfer plate, the fluid is allowed to flow relatively uniformly in the flow channel. Since the flow of each fluid is disturbed in the primary heat transfer enhancement surface and the auxiliary heat transfer enhancement surface, heat exchange can be enhanced. If the primary heat transfer enhancement surface is formed so that the longitudinal length thereof is equal to or smaller than two times the lateral length thereof, the amount of heat exchange can be increased while suppressing a pressure loss of the fluid at a small value.
Further, the drift suppressing rib set is arranged at irregular intervals. Therefore, at intermediate locations of the rib set where the fluid is essentially easy to flow, the flow of the fluid can be suppressed since the interval between the ribs located therein is narrow. On the other hand, at the ends of the rib set where the fluid is essentially hard to flow, the flow of the fluid can be accelerated since the interval between the ribs located therein is broad. Accordingly, the fluid can flow uniformly through the entire flow channel. This makes it possible to prevent a drift with reliability.
Furthermore, when the fluid providing heat exchange involving a phase change is used, the above-mentioned effect of decreasing a pressure loss in the flow channel can be exerted more remarkably.